Clay barely got past Doug Jones in his previous fight.
Sonny Banks had dropped him pretty hard about a year earlier.
It's not a HUGE surprise, in hindsight, that a man with a hook like Cooper in front of his home crowd, would put young Cassius down.
I think it's more remarkable that Liston could not do something similar in Clay's next fight.

I'd say Ali improved after his mistakes in the Cooper fight. He knew how dangerous Lison was, & would have prepared for it, physically & mentally. He needed to have done.

He did say that he only considered Cooper as a 'warm up' for the Liston fight.